1. Field of the Invention
The present invention relates to a liquid jetting apparatus such as an ink-jet printer and a recording method using the liquid jetting apparatus.
2. Description of the Related Art
A printer including an ink-jet head of a line-type in which a plurality of head units have been combined, has hitherto been known. These ink-jet heads include the plurality of head units. In each of the head units, a plurality of nozzles are arranged in rows in a width direction of a recording medium. The plurality of head units is arranged in a zigzag form along the width direction of the recording medium.
Two head units of the plurality of head units, which are adjacent in the width direction of the recording medium, are arranged such that end portions of the nozzle rows of the two head units overlap with each other. Moreover, in a range in which the two nozzle rows overlap, the nozzles in the two nozzle rows are located at the same positions in a nozzle-row direction, respectively. The range in which the nozzle rows of the two head units overlap is referred to as “an overlapping range”, in the following description. In a case that an image is recorded onto a recording medium by using nozzles in the overlapping range, one of the two types of nozzles for which the positions in the nozzle-row direction coincide, is to be used selectively.
In the abovementioned printer, there is a possibility that the positions of two head units are misaligned relatively in the width direction of the recording medium, or in other words, in the nozzle-row direction due to an assembling error of the head units. Ideally, the positions of the nozzles in the overlapping range should be aligned in the nozzle-row direction. However, the positions of the nozzles of two types in the overlapping range are misaligned. Accordingly, a distance between the dots formed on the recording medium by one of the two types of nozzles in the overlapping range and by the other type of nozzles in the overlapping range is either narrowed or widened. Accordingly, as compared to a case in which the two head units have been assembled without an error, there appears a portion in an image recorded on the recording medium, in which a density or concentration is high (dark) locally, and a portion in which the density is low (light) locally. Therefore, even in the conventional printer, a method has been devised such that the portion in which the density is high or low locally is not conspicuous.
In a certain printer as described above, in the overlapping range of the two nozzle rows, the two types of nozzles for jetting is switched or changed at a predetermined position in the overlapping range. Moreover, the predetermined position is not fixed. The aforementioned printer is configured to adjust the predetermined positions such that the predetermined positions differ at the time of forming each of a plurality of dot-rows aligned in a transporting direction. Accordingly, even when the two head units are misaligned, a position of the portion, in which the density is high or low locally and which appears in a portion of an image formed by nozzles near the predetermined position, is dispersed.
In another printer as described above, in the entire area of the overlapping range of the two nozzle rows, the nozzles which jet the ink are switched alternately in the nozzle-row direction. Accordingly, the switching positions of the two types of nozzles are dispersed in the entire area of the overlapping range. Therefore, the portion in which the density is high or low locally is not susceptible to be conspicuous.